Map Reduce程序在执行时会创建一个空目录

Question

我正在运行下面的Map reduce代码，以计算每个英语字母开头的单词的总和和平均长度。

For example : If the doc only contains the word 'and' 5 times
letter | total words | average length
   a        5               3

mapreduce程序如下：

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;


public class LetterWiseAvgLengthV1
{

    public static class TokenizerMapper
       extends Mapper<LongWritable, Text, Text, Text>
    {
        public void map(LongWritable key, Text value, Context context
                    ) throws IOException, InterruptedException
        {
            String st [] = value.toString().split("\\s+");          

            for(String word :  st) {

                String wordnew=word.replaceAll("[^a-zA-Z]",""); 
                String firstLetter = wordnew.substring(0, 1);

                if(!wordnew.isEmpty()){
                    // write ('a',3) if the word is and             
                    context.write(new Text(firstLetter), new Text(String.valueOf(wordnew.length())));                   
                }
                else continue; 
            }
        }
    }


    public static class IntSumReducer
       extends Reducer<Text,Text,Text,Text>
    {
        public void reduce(Text key, Iterable<Text> values,
                       Context context
                       ) throws IOException, InterruptedException
        {
            int sum=0,count=0;

            for (Text val : values)
            {
                sum += Integer.parseInt(val.toString());
                count+= 1;
            }

            float avg=(sum/(float)count);
            String op="Average length of " + count + " words = " + avg;
            context.write(new Text(key), new Text(op));
        }
    }




    public static void main(String[] args) throws Exception
    {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "wordLenAvgCombiner");

        job.setJarByClass(LetterWiseAvgLengthV1.class);

        job.setMapperClass(TokenizerMapper.class);
        job.setReducerClass(IntSumReducer.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

当我在文本文档上执行以下程序时，它将在HDFS中创建一个空的输出目录。执行期间没有失败，但输出文件夹始终为空